1. Field of the Invention
The present invention relates to a system for managing copyrights for using, storing, copying, editing, or transmitting digital data, particularly in multimedia applications.
2. Background Art
As database systems store increasingly larger amount of information, database systems are becoming popular in which many computers, used to store various types of data independently, are connected via communication lines to share the data.
In such a database system, the information handled up to this point has been conventionally coded information that can be processed by a computer, and that contains a relatively small amount of information and monochrome binary data, such as facsimile information at most. It is not possible to handle data containing a relatively large amount of information, such as data for natural pictures or animation. A technique is under development for digital processing of picture signals other than binary data, handled only as analog signals in the past.
By digitizing the picture signal, it is possible to handle a picture signal, e.g., a television signal, by a computer. "Multimedia systems" is an emerging technology of the future capable of simultaneously handling the data handled by computers and digitized picture data.
Because picture data contains an overwhelmingly large amount of information compared with character data and audio data, it is difficult to store or transfer or process the picture data by computer. For this reason, techniques for compressing or expanding picture data have been developed. Further, several standards for compression/expansion of picture data have been established. For example, the following standards have been established as common standards: JPEG (Joint Photographic image coding Experts Group) standards for still pictures, H.261 standards for video conferences, MPEG1 (Moving Picture image coding Experts Group 1) standards for picture accumulation, and MPEG2 standards for current television broadcasting and high definition television broadcasting. By using these new techniques, it is now possible to transmit digital picture data in real time.
For analog data, which has been widely used in the past, the control of copyrights during processing has not been an important issue because the quality of the analog data deteriorates each time the data is stored, copied, edited, or transferred. However, the quality of digital data does not deteriorate when the data is repeatedly stored, copied, edited, or transferred. Therefore, the management and control of copyrights during processing of digital data is an important issue.
Up to now, there has been no adequate method for management and control of copyrights for digital data. It has been managed and controlled merely by copyright law or by contracts. In copyright law, only compensation for digital sound or picture recording devices has been prescribed.
It is possible not only to refer to the content of a database, but also to effectively utilize the data obtained from the database by storing, copying, or editing the data, and also transferring the edited data to the database with the edited data registered as new data. Further, it is possible to transfer edited data to other persons via a communication link or by a proper recording medium.
In a conventional database system, only character data is handled. However, in multimedia systems, sound data and picture data originally generated as analog data, are digitized and used as part of the database in addition to the other data in the database such as character data.
Under such circumstances, it is an important question to determine how to control copyrights of the data in the database. However, there are no means in the prior art for copyright management and control of such actions as copying, editing, transferring, etc. of data.
The inventors of the present invention proposed in Japanese Patent Application 1994-46419 and Japanese Patent Application 1994-141004 a system for managing the copyrights wherein the user is required to obtain a permit key from the key control center through a public telephone line, and in Japanese Patent Application 1994-132916 an apparatus for this purpose.
The inventors also proposed in Japanese Patent Application 1994-64889 a copyright management method applicable to both the primary use of a database system such as displaying (including audio output) and storing of digital data and the secondary use such as copying, editing, and transmission, including the real-time transmission of digital picture. This database copyright management method provides in the database system a program and copyright information required to control the copyright in addition to a permit key which is transmitted to the user. The copyright management program monitors and manages to prevent users from operating beyond the conditions of users' request or permission.
The inventors also proposed in Japanese Patent Application 1994-237673 a database copyright management system for specifically implementing the database copyright management method proposed in Japanese Patent Application 1994-64889 described above.
The system proposed in Japanese Patent Application 1994-237673 comprises a key management center that manages a crypt key K and a copyright management center that manages the database copyright. According to this system, all the data delivered from a database is encrypted by a first crypt key K1, and a primary user who wishes to uses data directly from the database requests from the key management center the key K corresponding to the specific usage by presenting information I1 on the user to the center. In response to the primary usage request from the primary user, the key management center transfers the information I1 on the user to the copyright management center. On receiving the information I1, the copyright management center transfers this information I1 with a copyright management program Pc to the key control center. On receiving the copyright management program Pc, the key control center transfers the first crypt key K1 and a second crypt key K2 corresponding to the specific usage together with the copyright management program Pc to the primary user via a communication network. On receiving the first crypt key K1, the primary user uses this key to decrypt the data. The user subsequently uses the second crypt key K2 to encrypt and decrypt data when storing, copying or transmitting the data.
In cryptographic systems, the use of the crypt key K to encrypt a plaintext M to obtain a cryptogram C is expressed as: EQU C=E(K, M)
and the use of the crypt key K to decrypt the cryptogram C to obtain the plaintext M is expressed as: EQU M=D(K,C).
These conventions are followed hereafter in the specification.
If data is copied to an external recording medium or transmitted without being stored, the first and second crypt keys K1 and K2 are disused. If the primary user wishes to use the data again, the first and second crypt keys K1 and K2 are re-delivered to the user from the copyright management center. The re-delivery of the second crypt key K2 indicates that the data has been copied or transferred to a secondary user, and this is recorded in the copyright management center.
In requesting a secondary usage to the copyright management center, the secondary user presents the information I1 on the primary user and information I0 on the original copyright to the copyright management center. The copyright management center transmits to the secondary user a permit key Kp corresponding to the specific usage, together with a second crypt key K2 (viewing permit key), a third crypt key K3 (a permit key corresponding to the specific usage), and the copyright management program Pc which have been encrypted.
Typical encryption techniques include secret-key cryptosystem and public-key cryptosystem. The secret-key cryptosystem uses the same crypt key Ks for both encryption and decryption: EQU CmKs=E(Ks, M) EQU M=D(Ks, Cmks).
In the public-key cryptosystem, a key for encryption is open as a public-key, while a key for decryption is not open and is called a private-key. To use this cryptosystem, an information provider encrypts using the public-key Kb for a receiver: EQU Cmkb=E(Kb, M),
and the receiver decrypts the encrypted data using the private-key Kv that is not open: EQU M=D(Kv, Cmkb).
In the U.S. patent application Ser. No. 08/536,747, filed on Sep. 29, 1995, the inventors have proposed an invention that employs a first public-key Kb1, a first private-key Kv1 corresponding to the first public-key Kb1, a second public-key Kb2, and a second private-key Kv2 corresponding to the second public-key Kb2 that are prepared by the user, and a first secret-key Ks1 and a second secret-key Ks2 prepared by the database. The database uses the first secret-key Ks1 to encrypt data M: EQU Cmks1=E(Ks1, M)
and further encrypts the first secret-key Ks1 by the first public-key Kb1: EQU Cks1kb1=E(Kb1, Ks1)
and encrypts the second secret-key Ks2 by the second public-key Kb2: EQU Cks2kb2=E(Kb2, Ks2)
The database then transmits these encrypted data Cmks1 and the first and the second secret-keys CKs1kb1 and Cks2kb2 to the user. The user decrypts the first secret-key Cks1kb1 using the first private-key Kv1: EQU Ks1=D(Kv1, Cks1kb1),
and decrypts the encrypted data Cmks1 using the decrypted first secret-key Ks1: EQU M=D(Ks1, Cmks1)
and the encrypted second secret-key Cks2kb2 using the second private-key Kv2: EQU Ks2=D(Kv2, Cks2kb2)
The decrypted second secret-key Ks2 is used for storing, copying, and transferring data after data decryption.